1. Technical Field of the Invention
The present invention relates to a network system for transferring messages and various types of information among application programs or objects in a plurality of nodes, a network control method for controlling the network system, and a signal sender/receiver connected to the network system.
2. Prior Art
A conventional network system can transfer messages and various types of information among application programs or objects (referred to as a process hereafter for a broader term including all of these) in a plurality of nodes. For example, such a network uses the following method to determine a server or a server process. A process having capabilities that can provide a server attempts to find a server currently available on the network using a simple broadcast that specifies no destinations in the network. When not finding an available server, that process itself becomes a server.
Accordingly, when a process (called a client process) other than servers on the network performs some processing, the client process first finds a server process on the network using the above-mentioned broadcast. That client process sends a request to the server process to perform necessary processing.
Determination of a server process using the above-mentioned simple broadcast is frequently applied, for example, when power is turned on for a node on the network, when a node is newly connected to the network, or when a node on the network enters a processing instruction.
[Problems to be Solved by the Invention]
As mentioned above, the conventional network system determines a server process using the simple broadcast without specifying destinations. It is impracticable to apply the method for determining a server process using the simple broadcast to a large-scale network that connects more than tens of thousands of processes because determining the server process requires a long time. In other words, determination of a server process using the simple broadcast is applicable for only a small-scale network with a limited range to search for server processes.
Further, as mentioned above, the conventional network system determines a server process using the simple broadcast, for example, when power is turned on, when a connection is made to the network, or when a processing instruction is entered. If an error occurs on the server process, for example, each client process can be notified of an error occurrence on the server process only when a server process is determined, namely when power is turned on, when a connection is made to the network, or when a processing instruction is entered. It is impossible to early detect the error occurrence on the server process, thus requiring a time delay before recovering the error or starting a recovery action. In other words, each client process is subject to restrictions on network processing until the server process recovers from the error.
The present invention takes these situations into consideration. It is an object of the present invention to provide a network system, a network control method, and a signal sender/receiver that can flexibly comply with various network configurations and allow each process to continue necessary processing even if a network error occurs.